In recent years, importance of sustainable conservation of global environments has been recognized and industrial systems, traffic systems, products, etc. capable of minimizing the use of fossil fuels have been developed vigorously. Such environmental feasible systems and products include, for example, wind power generation systems, railway systems, hybridcars, and electric cars.
Main devices used for such environmental feasible systems and products include highly efficient rotary electric machines (motors and generators). Magnets containing rare-earth elements (so-called rare-earth magnets) are used for the highly efficient rotary electric machines. For example, rare-earth magnets used for highly efficient rotary electric machines of hybrid cars are required to have high coercive force even under high temperature environments, for which rare-earth magnets containing rare earth elements such as neodymium (Nd) or dysprosium (Dy) have been used. At present, rare-earth magnets are indispensable for highly efficient rotary electric machines and further expansion of demand is expected in the feature.
On the other hand, due to increase in the cost of rare-earth materials caused by geographical localization of rare-earth material resources, methods of decreasing the amount of rare-earth ingredients used in the rare-earth magnets and methods for separating and recovering rare-earth elements from spent rare-earth magnets have been investigated. Examples of the separation and recovery method include a method for separating and recovering rare earth elements from cutting dusts (sludges) generated in production process of rare-earth elements and from magnet wastes.
As a method for separating and recovering rare-earth elements from compositions containing plural kinds of rare-earth elements (hereinafter referred to as “rare-earth compositions”) such as rare-earth magnets, Document 1 discloses a separation method utilizing the difference of solubility between sulfates of neodymium (Nd) and dysprosium (Dy). Document 2 discloses a method of leaching sludges with an acid and then applying solvent extraction. Document 3 discloses a method of halogenizing rare-earth elements in a mixture containing plural kinds of rare-earth elements or compounds thereof, thereby separating bivalent rare-earth halides and trivalent rare-earth halides by utilizing the difference of properties between them. Further, Document 4 discloses a method of reacting sludges or magnet wastes with iron chlorides and separating and recovering rare-earth elements as chlorides.